Is Pregnancy Risky for You?

During pregnancy, women's breasts are exposed to large amounts of estrogen and other hormones that may prompt the growth of some breast cancers. What is your outlook if you develop breast cancer during pregnancy or shortly after giving birth? How do your chances of surviving the cancer compare to those a non-pregnant woman who develops breast cancer? Do the hormones of pregnancy make it harder to successfully treat breast cancer?

And, if you have a personal history of breast cancer, will pregnancy increase the risk of the breast cancer coming back (recurring)?

Pregnancy does not lower survival or increase the risk of recurrence

For women with a personal history of breast cancer, studies have shown that:

• There was no apparent long-term increased risk of cancer recurrence or death in women who became pregnant after a breast cancer diagnosis.
• Pregnancy did not appear to cause new cancers to develop.
• Women who were diagnosed with breast cancer during pregnancy did as well in the long term as women with the same type and stage of cancer who were not pregnant when they were diagnosed.

Breast cancer during pregnancy responds well to treatment

How well and long pregnant women live after breast cancer depends on the nature of the disease and the stage at which it is diagnosed. (This is also true for women who aren't pregnant with breast cancer.) Treatment is more likely to be effective for cancers diagnosed before they spread beyond the breast or have reached a large size. "Personality features" of the cancer are also important in predicting response to treatment and long-term survival. (See below.)

Women diagnosed with breast cancer during pregnancy tend to have more advanced cancers at diagnosis than other women with breast cancer. Because of this, many doctors in the past assumed pregnant women with breast cancer would respond poorly to treatment. But most studies show that they respond as well as other women of the same age and with the same stage and type of breast cancer.

Research is limited

Still, it's important to remember that the safety of pregnancy for women with breast cancer, or who have been treated for breast cancer, is not easy to study. It's nearly impossible to find women with the same cancer status and fertility outcomes, who can be compared in randomized clinical trials.

Available information on pregnancy safety comes from studies that are retrospective (looking at past history). In these studies, researchers looked at the medical records of pre-menopausal women (women who were still having their periods) with a personal history of breast cancer. They then compared the outcomes of women who were pregnant at diagnosis, or who became pregnant after being diagnosed, to those of women who did not become pregnant.

Keep in mind also that the number of women included in these studies is very small — only a few hundred in all of them put together. New research on these issues could change what we currently know.

"Personality" of breast cancer during pregnancy

There are many different kinds of breast cancer, each with its own "personality." What types of breast cancers tend to arise during or shortly after pregnancy? Are they more or less aggressive than other breast cancers? Are they more or less likely to respond to certain treatments?

Studies have found that the types of breast cancer that arise during or shortly after pregnancy are very similar to breast cancers in women who are not pregnant. Most breast cancers, in general, start in the milk ducts of the breast rather than in the milk-producing glands (lobules) of the breast. Studies suggest that this is also true for breast cancers that arise during pregnancy.

Some studies have suggested that breast cancers diagnosed in pregnant women were more likely to have spread to sites outside the breast by the time they're detected. This could be because the increased blood flow and hormone levels in pregnant women make it easier for breast cancers to spread. Another explanation is a delay in the diagnosis of breast cancers in pregnant women. Breast lumps that appear during pregnancy may be mistaken for normal breast changes due to pregnancy, and not due to cancer. For that reason, women or their doctors may delay getting a biopsy until after the cancer has become large or has spread.

Hormone receptor status

Another personality feature of breast cancers is their hormone receptor status. Breast cancers with hormone receptors tend to respond well to treatment called hormonal therapy.

Several studies have found that breast cancers are more likely to be hormone-receptor-negative (without hormone receptors) in pregnant than in non-pregnant women. It's possible, however, that the cancers in pregnant women actually do have hormone receptors, but these may not be detected because of the high levels of hormones during pregnancy or the tests used to determine hormone receptors status.

To measure hormone receptors, lab technicians usually do what is called a "ligand-binding assay." With this test the technician exposes tumor samples to the hormones estrogen or progesterone. Then he or she measures how much of the hormones latches on to cancer cells' hormone receptors.

But in pregnant women, many of those receptor "slots" are already filled with the high amounts of hormones that travel in the blood during pregnancy.

In addition, when there are high levels of hormones in the body, the hormone receptors get overwhelmed with too many hormones "yelling in their ears." So the cells might shut down their hormone receptors to avoid all the "noise." When the hormone receptors are shut down, they can't be counted.

For these reasons, the test for hormone receptors in a pregnant woman could show no receptors, even though the cancer may still respond to hormone therapy after pregnancy is over. More recently, technicians have started using a different test to find the hormone receptor status of breast cancers. This test, called "immunohistochemical (IHC) staining assay" uses antibodies to detect estrogen receptors on tumor cells. The amounts of hormones traveling in the blood do not affect the accuracy of this test.

One study found that some cancers taken from pregnant women that tested hormone-receptor-NEGATIVE in a ligand-binding assay, tested hormone-receptor-POSITIVE in an IHC assay.

If you're diagnosed during pregnancy and your pathology report says the cancer is hormone-receptor-negative, ask your doctor which test was used to determine this. If it was a ligand-binding assay, ask to have the tissue re-tested with IHC. This is important because it may affect which treatments you get after the pregnancy is over.

HER2 status

Another important trait of breast cancers is their HER2 status (also called HER2/neu status). Cancers with too many copies of the HER2 gene, or too many HER2 receptors, tend to grow fast. They are also associated with an increased risk of spread. But they can respond very well to medicines that works against HER2.

There are three tests for HER2 status: IHC (immunohistochemistry), FISH (Fluorescence In Situ Hybridization), and SPoT-Light HER2 CISH (Subtraction Probe Technology Chromogenic In Situ Hybridization). In pregnant women, the accuracy of the IHC test for HER2 may be limited, because the blood levels of the HER2 protein normally increase as pregnancy progresses. This means the IHC test for HER2 may show that the cancer is HER2-positive when in fact the cancer is HER2-negative.

The FISH and SPoT-Light tests are more reliable ways to test HER2 status in all women, including pregnant women. If you are diagnosed with breast cancer during pregnancy, ask to have the HER2 status of the cancer determined with a FISH or SPoT-Light test.